768 research outputs found
The production of charm mesons from quark matter at CERN SPS and RHIC
We study the production of charm mesons and other charm baryons from quark
matter at CERN SPS and RHIC energies. Using quark coalescence models as
hadronization mechanism, we predict particle ratios, absolute yields and
transverse momentum spectra.Comment: 4 pages in Latex, 2 PS figure, to be published in the proceedings of
the SQM'2000 Conference, Berkeley, CA, July 20-25, 2000. Submitted to J.
Phys.
Generating new solutions for relativistic transverse flow at the softest point
Using the method of prolongation we generate new solutions from a simple
particular solution for relativistic transverse flow with cylindrical symmetry
in 1+3 dimensions. This is an extension of the longitudinal Bjorken flow ansatz
and can be applied among others during first order phase transition in an
expanding system. The prolongated solution allows for tracing back the flow
profile from a transverse flow conjectured at the end of phase transition at
CERN SPS heavy ion collisons.Comment: 11 pages LaTeX, 1 ps figur
Analytic solution for relativistic transverse flow at the softest point
We obtain an extension of Bjorken's 1+1 dimensional scaling relativistic flow
solution to relativistic transverse velocities with cylindrical symmetry in 1+3
dimensions at constant, homogeneous pressure (vanishing sound velocity). This
can be the situation during a first order phase transition converting quark
matter into hadron matter in relativistic heavy ion collisions.Comment: 9 pages LaTeX, 1 .eps figure, Figure replaced by another presentation
showing contour-lines of QGP-hadron phase mixtures in the longitudinal time -
transverse radius plane. To appear in Phys.Lett.
The Anticorrelated Nature of the Primary and Secondary Eclipse Timing Variations for the Kepler Contact Binaries
We report on a study of eclipse timing variations in contact binary systems,
using long-cadence lightcurves in the Kepler archive. As a first step,
'observed minus calculated' (O-C) curves were produced for both the primary and
secondary eclipses of some 2000 Kepler binaries. We find ~390 short-period
binaries with O-C curves that exhibit (i) random-walk like variations or
quasi-periodicities, with typical amplitudes of +/- 200-300 seconds, and (ii)
anticorrelations between the primary and secondary eclipse timing variations.
We present a detailed analysis and results for 32 of these binaries with
orbital periods in the range of 0.35 +/- 0.05 days. The anticorrelations
observed in their O-C curves cannot be explained by a model involving mass
transfer, which among other things requires implausibly high rates of ~0.01
M_sun per year. We show that the anticorrelated behavior, the amplitude of the
O-C delays, and the overall random-walk like behavior can be explained by the
presence of a starspot that is continuously visible around the orbit and slowly
changes its longitude on timescales of weeks to months. The quasi-periods of
~50-200 days observed in the O-C curves suggest values for k, the coefficient
of the latitude dependence of the stellar differential rotation, of
~0.003-0.013.Comment: Published in The Astrophysical Journal, 2013, Vol. 774, p.81; 14
pages, 12 figures, and 2 table
Simple predictions from ALCOR_c for rehadronisation of charmed quark matter
We study the production of charmed hadrons with the help of ALCOR_c, the
algebraic coalescence model for rehadronisation of charmed quark matter.
Mesonic ratios are introduced as factors connecting various antibaryon to
baryon ratios. The resulting simple relations could serve as tests of quark
matter formation and coalescence type rehadronization in heavy ion collisions.Comment: 7 pages in Latex, 1 PS figur
Experiment-based Comparison of Prediction Methods for Pump Head Degradation with Viscous and Power-law Fluids
Although several methods are known to calculate pump performance with highly viscous and non-Newtonian fluids, research has not yet determined all the key parameters of these predictions. It is unclear how these parameters depend on the pump geometry and the delivered fluid rheology, which can vary widely in the chemical industry. In our study, the performance curves of a radial centrifugal pump with a viscous Newtonian glycerol solution and a non-Newtonian power-law fluid were experimentally compared. The head degradation of the pump was also presumed with the ANSI/HI and the Ofuchi methods, which are evident and commonly used for viscous Newtonian fluids, but not for non-Newtonians. The required constants were estimated based on experimental data
for both models, and the Ofuchi method was adapted to power-law fluid. Based on our results, the Ofuchi method proved to apply for head degradation prediction with the examined power-law fluid.
This work is licensed under a Creative Commons Attribution 4.0 International License
Interplay of tidal evolution and stellar wind braking in the rotation of stars hosting massive close-in planets
This paper deals with the application of the creep tide theory (Ferraz-Mello,
Cel. Mech. Dyn. Astron. vol. 116, 109, 2013) to the study of the rotation of
stars hosting massive close-in planets. The stars have nearly the same tidal
relaxation factors as gaseous planets and the evolution of their rotation is
similar to that of close-in hot Jupiters: they tidally evolve towards a
stationary solution. However, stellar rotation may also be affected by stellar
wind braking. Thus, while the rotation of a quiet host star evolves towards a
stationary attractor with a frequency () times the orbital mean-motion
of the companion, the continuous loss of angular momentum in an active star
displaces the stationary solution towards slower values: Active host stars with
big close-in companions tend to have rotational periods larger than the orbital
periods of their companions. The study of some hypothetical examples shows that
because of tidal evolution, the rules of gyrochronology cannot be used to
estimate the age of one system with a large close-in companion, no matter if
the star is quiet or active, if the current semi-major axis of the companion is
smaller than 0.03--0.04 AU. Details on the evolution of the systems: CoRoT
LRc06E21637, CoRoT-27, Kepler-75, CoRoT-2, CoRoT-18, CoRoT-14 and on
hypothetical systems with planets of mass 1--4 M_Jup in orbit around a star
similar to the Sun are given.Comment: 22 pages, 8 figures; Publication in Ap
Probing the atmosphere of a sub-Jovian planet orbiting a cool dwarf
We derive the 0.01 m binned transmission spectrum, between 0.74 and 1.0
m, of WASP-80b from low resolution spectra obtained with the FORS2
instrument attached to ESO's Very Large Telescope. The combination of the fact
that WASP-80 is an active star, together with instrumental and telluric
factors, introduces correlated noise in the observed transit light curves,
which we treat quantitatively using Gaussian Processes. Comparison of our
results together with those from previous studies, to theoretically calculated
models reveals an equilibrium temperature in agreement with the previously
measured value of 825K, and a sub-solar metallicity, as well as an atmosphere
depleted of molecular species with absorption bands in the IR ().
Our transmission spectrum alone shows evidence for additional absorption from
the potassium core and wing, whereby its presence is detected from analysis of
narrow 0.003 m bin light curves (). Further observations with
visible and near-UV filters will be required to expand this spectrum and
provide more in-depth knowledge of the atmosphere. These detections are only
made possible through an instrument-dependent baseline model and a careful
analysis of systematics in the data.Comment: 13 pages, 11 figures, 3 tables. Accepted for publication in MNRA
An estimate of the Love number of WASP-18Ab from its radial velocity measurements
Context. Increasing our knowledge of the interior structure, composition and
density distribution of exoplanets is crucial to make progress in the
understanding of exoplanetary formation, migration and habitability. However,
the directly measurable mass and radius values offer little constraint on
interior structure, because the inverse problem is highly degenerate. Therefore
there is a clear need for a third observable of exoplanet interiors. This third
observable can be the fluid Love number which measures the central mass
concentration of an exoplanet. Aims. The aims of this paper are (i) to develop
a basic model to fit the long-term radial velocity and TTV variations caused by
tidal interactions, (ii) to apply the model to the WASP-18Ab system, and (iii)
to estimate the Love number of the planet. Methods. Archival radial velocity,
transit and occultation timing data are collected and fitted via the model
introduced here. Results. The best model fit to the archival radial velocity
and timing data of WASP-18Ab was obtained with a Love number of the massive
() hot Jupiter WASP-18Ab: . This causes apsidal motion in the system, at a rate of
arcseconds/day. When checking possible causes of periastron precession, other
than the relativistic term or the non-spherical shape of the components, we
found a companion star to the WASP-18 system, named WASP-18B which is a
probable M6.5V dwarf with at 3519 AU distance from the
transit host star. We also find that small orbital eccentricities may be real,
rather than an apparent effect caused by the non spherical stellar shape.Comment: Accepted for publication in Astronomy and Astrophysic
On the Use of Multipole Expansion in Time Evolution of Non-linear Dynamical Systems and Some Surprises Related to Superradiance
A new numerical method is introduced to study the problem of time evolution
of generic non-linear dynamical systems in four-dimensional spacetimes. It is
assumed that the time level surfaces are foliated by a one-parameter family of
codimension two compact surfaces with no boundary and which are conformal to a
Riemannian manifold C. The method is based on the use of a multipole expansion
determined uniquely by the induced metric structure on C. The approach is fully
spectral in the angular directions. The dynamics in the complementary 1+1
Lorentzian spacetime is followed by making use of a fourth order finite
differencing scheme with adaptive mesh refinement.
In checking the reliability of the introduced new method the evolution of a
massless scalar field on a fixed Kerr spacetime is investigated. In particular,
the angular distribution of the evolving field in to be superradiant scattering
is studied. The primary aim was to check the validity of some of the recent
arguments claiming that the Penrose process, or its field theoretical
correspondence---superradiance---does play crucial role in jet formation in
black hole spacetimes while matter accretes onto the central object. Our
findings appear to be on contrary to these claims as the angular dependence of
a to be superradiant scattering of a massless scalar field does not show any
preference of the axis of rotation. In addition, the process of superradiance,
in case of a massless scalar field, was also investigated. On contrary to the
general expectations no energy extraction from black hole was found even though
the incident wave packets was fine tuned to be maximally superradiant. Instead
of energy extraction the to be superradiant part of the incident wave packet
fails to reach the ergoregion rather it suffers a total reflection which
appears to be a new phenomenon.Comment: 49 pages, 11 figure
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